One of the objects to be achieved in controlling technological processes is to maintain an output parameter of the process at a desired level, which is usually accomplished by the use of an automatic controller. The parameters of the controller are chosen so as to provide the best control quality. Since, the conditions under which the controlled process is conducted and the process characteristics vary in the course of operation of the controller, the initially chosen parameters of the controller may cease to be optimal, from the standpoint of optimal control quality. For example, if the temperature in a chemical reactor is to be automatically controlled, variations in the chemical composition or quantity of the starting materials will affect the rate of chemical reaction and other characteristics of the controlled process thus necessitating readjustment of the controller in order to achieve the best control quality.
Known in the art is a method of controlling a technological process by maintaining an output parameter of the process at a desired level with the aid of an automatic controller, comprising the steps of measuring an index of control quality and varying the parameters of the controller so as to achieve the best control quality (cf. a book "Avtomatizatsiya proizvodstva i promyshlennaya elektronika", vol. 3, edited by A. I. Berg and V. A. Trapeznikov, published by "Sovetskaya Entsiklopediya", Moscow, 1962, p. 297). According to this method, the best control quality is achieved by varying the parameter of the controller which affects the index of control quality so that the latter represents an optimal function of the controller parameter. This parameter is varied in a direction causing the index of control quality to vary towards improvement of the control quality until an optimal value of the index corresponding to the best control quality is reached. If the variation of the controller parameter leads to a decline in control quality, the direction of variation of the controller parameter is reversed. Such variation of the controller parameter makes it possible to achieve better control quality when controlling a process under varying conditions and thus ensures a higher accuracy of control of the output parameter of the process.
Variation of the controller parameter at least in one direction usually leads to reduction in the stability margin of the automatic control system. Therefore, the variation of this parameter should be carried out so as not to cause the system to become unstable.
The known method can be carried out by the use of a known automatic control apparatus comprising an automatic controller for maintaining an output parameter of a technological process at a desired level, a control quality signal generating device for generating a signal representative of an index of control quality, a control signal generating circuit for generating a control signal depending on variation of the signal representative of the index of control quality, and a parameter adjusting device connected to the output of the control signal generating circuit for adjusting a parameter of the automatic controller (cf. the above-cited reference, p. 296, FIG. 6).
Greater time is required for adjustment of the controller parameter to a value which ensures the best control quality, the greater the deviation of the index of control quality from an optimum value and the longer the time lag of the controlled equipment. Therefore, in the event of a large deviation of the index of control quality from its optimum value in control systems, wherein the controlled equipment has a considerable time lag (e.g. several minutes), the adjustment of the controller parameter will be rather slow, which will lead to substantial reduction in the control accuracy when the process is conducted under varying conditions.